Palaeoglaciology 1: landsystems

Question 1

What is the inversion concept?

Answer 1

the idea that using landforms to reconstruct the characteristics of the past ice sheet can also be inverted to use the knowledge of ice sheets today to know how landforms were created previously

Question 2

What are landsystems?

Answer 2

common terrains attributes of topography, soils and vegetation that reflect an underlying geology, past erosional and depositional processes and climate

Question 3

What are the components of a landsystem?

Answer 3

Elements = individual landforms
Units = groups of elements
Landsystems = recurrent patterns between different units

Question 4

What is a glacier surge?

Answer 4

A multi-year oscillation between extended periods of normal motion and brief periods of comparatively fast motion (Raymond, 1987)

Question 5

Why do surges happen?

Answer 5

An excess of accumulation above that which normal flow cannot discharge thereby causing it to increase which is known as a ‘surge’

Question 6

What are the two phases/states of surge glaciers?

Answer 6

Active = rapid (10-100x faster) flow that can last as little as 1-5 years occurring every 10-200 years
Quiescent = slow motion between the active phases

Question 7

What are the two hypothesised triggers for a glacier surge?

Answer 7

1) collapse of drainage tunnels releases trapped water leading to building up of pressure that releases meltwater supply to bed that causes detachment and sliding
2) Water drainage through permeable subglacial sediment, permeability reduces ice thickness which causes the ice pressure to accumulate and then initiates rapid motion

Question 8

How many characteristic landform types do terrestrial landsystems have? Who said this?

Answer 8

8 - Evans et al. 1999

Question 9

What are the 8 landform types divided in to?

Answer 9

4 formed during active phase

4 formed during quiescent phase

Question 10

What are flutes?

Answer 10

small-scale linear features

Question 11

How do flutes form?

Answer 11

when the glacier surges it will have a boulder embedded in its base that deforms resulting in a flute of sediment within a cavity as it moves forward.

Question 12

What are overridden moraines and how are they formed?

Answer 12

during the surge over a foreland, pre-existing moraine ridges formed by previous surges are overridden by the glacier which creates a domed hill over the top.

Question 13

What are the overridden moraines covered with?

Answer 13

A carapace of subglacial till that it smoothed out into fluted mounds

Question 14

What are glaciotectonic composite ridges?

Answer 14

Sediment wedges that form during a glacier surge and then pile on top of each other during successive surges

Question 15

How do glaciotectonic composite ridges form?

Answer 15

During advance at the termination of the surge the glacier surge thrusts proglacial sediments in to ridges that solidify as wedges

Question 16

What are blowout structures and how do they form?

Answer 16

As a result of the build up of subglacial meltwater before a surge, when it surges the meltwater can be ejected violently through a blow out that can also create a hole in the landscape.

Question 17

What are hummocky moraines and how are they formed?

Answer 17

During the active phase a lot of water and sediment accumulate at the snout of the glacier. At the end of this phase ice blocks melt out and can be left at the ice-marginal position. Eventually the ice will melt leaving debris to melt out the ice

Question 18

How are outwash tracks formed and what are they?

Answer 18

At the end of surge phase and through following quiescent phase, proglacial outwash occurs and small proglacial lakes form at the snout. Glaciofluvial sediment is then deposited here at the end of the phase. The channels and lakes infill outwash tracks of stagnant ice blocks with sediment

Question 19

What are concertina eskers?

Answer 19

Zig-zaged eskers

Question 20

How do concertina eskers form?

Answer 20

When an englacial or subglacial channel that carries both water and sediment deposits it material and the ice melts away. The zig zag shape derives from how the channels were forced to find the path of least resistance when they were active which involves joining up lots of small englacial channels and the since deformation that has occurred to the glacier

Question 21

What are crevasse squeeze ridges and how do they form?

Answer 21

During a surge sediment will be forced upwards in to crevasses within the ice. when the ice then retreats it needs to do so slowly so that these ridges are then preserved